I have some serious questions as to the health of your kitten. NO kitten should EVER be weaned at 3 to 4 weeks! This is so wrong it's almost criminal. If weaned, what was the replacement food that was given? It better have been KMR (Kitten Milk Replacement). Kittens are born only knowing how to nurse not to chew so what food was given to the kitten? Even at 6 to 8 weeks some kittens teeth and jaws are not strong enough to eat kitten kibble that's why kibble is mixed with formula to make it into a mush so they can lick it up. Even then some have to be spoon fed because they don't know how to eat.
Reputable breeders and cat people would never separate a kitten from its mother until the kitten is 10 to 12 weeks old because the mom is training the kitten in how to be a cat. For a totally psychologically sound adult animal it should be with mom until that time. The people who are "caring" for these animals are doing a poor job as far as I'm concerned.
The kitten MUST be blood tested for FIV and FeLV. If FIV positive it can live indoors with no other cats and with a stress free and consistent vet care it will have a happy life. If it is positive for FeLV that's fatal and the kitten needs to be put down. It MUST be dewormed, do not do it yourself with OTC stuff because too much damage and harm to the animal can occur. The kitten should NEVER have been treated for fleas at this age. Again, I question the intelligence of the people handling these animals! They can't be treated until they at least 8 weeks old or it can kill them!
If the kitten is going to live indoors and only go outside in a carrier to vet appts then in reality it doesn't need any shots at all including rabies because some preventative shots can cause harm. If it will have any access to outside then every shot the vet has it needs including for URI (Upper Respiratory Infection). It cannot be treated for fleas until it is 8 weeks old and then it should be getting the kitten dosage of Advantage. Don't use flea soaps, sprays, collars, powder, or pills!
1. Talk to your vet about vaccinations after you decide if it will be indoor or outdoor. Your vet will tell you when, if you decide to do it. At 4 month old it needs to be spayed and microchipped. Don't wait!
2. You need a kitten size litter box at first, sides are much lower. At about 6 months you should be able to transfer to regular size litterbox.
3. Your kitten needs kitten food ONLY until it is 1 year old. Kitten kibble and canned kitten food. It should be still eating kitten kibble made into mush with formula at this stage. Never give a cat cow's milk. Most cats are lactose intolerant and will get diarrhea. Goat's milk from dairy sec at the grocery store is okay.
4. You don't need to bathe a cat ever. They clean themselves. If you have an outdoor cat which you should not but if that's what you decide use only a mild shampoo such as baby shampoo or Dawn (only this brand!) dishwashing soap.
5. Don't allow the kitten to roam! Keep it warm, keep it in one room for the next few weeks. Keep toilet lids down as they can drown in there! Keep dryer doors closed as they will go in to sleep and die when you turn it on. Supervise closely if you have a recliner chair as kittens climb up inside furniture and if you recline the chair you can kill it. Do not let the kitten stay in a room unsupervised when you have it out to play.
http://www.2ndchance.info/orphankitten.htm - what should have been done
http://pets.webmd.com/cats/ss/slideshow-foods-your-cat-should-never-eat - food never to feed
http://cats.about.com/cs/kittencare/a/kitcareone.htm
http://cats.about.com/cs/kittencare/a/kitcareone.htm - kitten care
http://www.vetstreet.com/cats/bringing-a-new-kitten-home - what you need
http://www.timberkatz.com/Kitten-Development-Stages.php - as kitten grows
http://www.youtube.com/watch?v=5YLDQMvskH8 - clipping nails video
http://www.youtube.com/watch?v=FWFKl_rSpM8 - scruff video